This commit adds a trivial textbook implementation of preemptible RCU
to rcutorture ("torture_type=trivial-preempt"), similar in spirit to the
existing "torture_type=trivial" textbook implementation of non-preemptible
RCU. Neither trivial RCU implementation has any value for production use,
and are intended only to keep Paul honest in his introductory writings
and presentations.
[ paulmck: Apply kernel test robot feedback. ]
---
include/linux/sched.h | 4 ++
kernel/rcu/Kconfig.debug | 11 ++++
kernel/rcu/rcu.h | 4 ++
kernel/rcu/rcutorture.c | 57 ++++++++++++++++++-
kernel/rcu/update.c | 22 +++++++
.../rcutorture/configs/rcu/TRIVIAL-PREEMPT | 12 ++++
.../configs/rcu/TRIVIAL-PREEMPT.boot | 3 +
7 files changed, 112 insertions(+), 1 deletion(-)
create mode 100644
tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL-PREEMPT
create mode 100644
tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL-PREEMPT.boot
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 074ad4ef3d813..fc2cb6804eabe 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -948,6 +948,10 @@ struct task_struct {
struct srcu_ctr __percpu *trc_reader_scp;
#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
+#ifdef CONFIG_TRIVIAL_PREEMPT_RCU
+ int rcu_trivial_preempt_nesting;
+#endif /* #ifdef CONFIG_TRIVIAL_PREEMPT_RCU */
+
struct sched_info sched_info;
struct list_head tasks;
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 625d75392647b..e078e988773d6 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -228,4 +228,15 @@ config RCU_DYNTICKS_TORTURE
This has no value for production and is only for testing.
+config TRIVIAL_PREEMPT_RCU
+ bool "Textbook trivial preemptible RCU in rcutorture"
+ depends on RCU_EXPERT && RCU_TORTURE_TEST
+ default n
+ help
+ This option enables a textbook preemptible RCU that is
+ implemented in rcutorture. Its sole purpose is to validate
+ code used in books, papers, and presentations.
+
+ This has no value for production and is only for testing.
+
endmenu # "RCU Debugging"
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index dc5d614b372c1..37e7a8a9e375d 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -682,4 +682,8 @@ int rcu_stall_notifier_call_chain(unsigned long val, void
*v);
static inline int rcu_stall_notifier_call_chain(unsigned long val, void *v) {
return NOTIFY_DONE; }
#endif // #else // #if defined(CONFIG_RCU_STALL_COMMON) &&
defined(CONFIG_RCU_CPU_STALL_NOTIFIER)
+#ifdef CONFIG_TRIVIAL_PREEMPT_RCU
+void synchronize_rcu_trivial_preempt(void);
+#endif // #ifdef CONFIG_TRIVIAL_PREEMPT_RCU
+
#endif /* __LINUX_RCU_H */
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 8a9282a0245cc..3c272413666b2 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1061,6 +1061,61 @@ static struct rcu_torture_ops trivial_ops = {
.name = "trivial"
};
+#ifdef CONFIG_TRIVIAL_PREEMPT_RCU
+
+/*
+ * Definitions for trivial CONFIG_PREEMPT=y torture testing. This
+ * implementation does not work well with large numbers of tasks or with
+ * long-term preemption. Either or both get you RCU CPU stall warnings.
+ */
+
+static void rcu_sync_torture_init_trivial_preempt(void)
+{
+ rcu_sync_torture_init();
+ if (WARN_ONCE(onoff_interval || shuffle_interval, "%s: Non-zero
onoff_interval (%d) or shuffle_interval (%d) breaks trivial RCU, resetting to
zero", __func__, onoff_interval, shuffle_interval)) {
+ onoff_interval = 0;
+ shuffle_interval = 0;
+ }
+}
+
+static int rcu_torture_read_lock_trivial_preempt(void)
+{
+ struct task_struct *t = current;
+
+ WRITE_ONCE(t->rcu_trivial_preempt_nesting,
t->rcu_trivial_preempt_nesting + 1);
+ smp_mb();
+ return 0;
+}
+
+static void rcu_torture_read_unlock_trivial_preempt(int idx)
+{
+ struct task_struct *t = current;
+
+ smp_store_release(&t->rcu_trivial_preempt_nesting,
t->rcu_trivial_preempt_nesting - 1);
+}
+
+static struct rcu_torture_ops trivial_preempt_ops = {
+ .ttype = RCU_TRIVIAL_FLAVOR,
+ .init = rcu_sync_torture_init_trivial_preempt,
+ .readlock = rcu_torture_read_lock_trivial_preempt,
+ .read_delay = rcu_read_delay, // just reuse rcu's version.
+ .readunlock = rcu_torture_read_unlock_trivial_preempt,
+ .readlock_held = torture_readlock_not_held,
+ .get_gp_seq = rcu_no_completed,
+ .sync = synchronize_rcu_trivial_preempt,
+ .exp_sync = synchronize_rcu_trivial_preempt,
+ .irq_capable = 0, // In theory it should be, but let's keep it
trivial.
+ .name = "trivial-preempt"
+};
+
+#define TRIVIAL_PREEMPT_OPS &trivial_preempt_ops,
+
+#else // #ifdef CONFIG_TRIVIAL_PREEMPT_RCU
+
+#define TRIVIAL_PREEMPT_OPS
+
+#endif // #else // #ifdef CONFIG_TRIVIAL_PREEMPT_RCU
+
#ifdef CONFIG_TASKS_RCU
/*
@@ -4449,7 +4504,7 @@ rcu_torture_init(void)
static struct rcu_torture_ops *torture_ops[] = {
&rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops,
&busted_srcud_ops,
TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
- &trivial_ops,
+ &trivial_ops, TRIVIAL_PREEMPT_OPS
};
if (!torture_init_begin(torture_type, verbose))
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index d98a5c38e19c5..b62735a678842 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -538,6 +538,28 @@ long torture_sched_setaffinity(pid_t pid, const struct
cpumask *in_mask, bool do
EXPORT_SYMBOL_GPL(torture_sched_setaffinity);
#endif
+#if IS_ENABLED(CONFIG_TRIVIAL_PREEMPT_RCU)
+// Trivial and stupid grace-period wait. Defined here so that lockdep
+// kernels can find tasklist_lock.
+void synchronize_rcu_trivial_preempt(void)
+{
+ struct task_struct *g;
+ struct task_struct *t;
+
+ smp_mb(); // Order prior accesses before grace-period start.
+ rcu_read_lock(); // Protect task list.
+ for_each_process_thread(g, t) {
+ if (t == current)
+ continue; // Don't deadlock on ourselves!
+ // Order later rcu_read_lock() on other tasks after QS.
+ while (smp_load_acquire(&t->rcu_trivial_preempt_nesting))
+ continue;
+ }
+ rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_trivial_preempt);
+#endif // #if IS_ENABLED(CONFIG_TRIVIAL_PREEMPT_RCU)
+
int rcu_cpu_stall_notifiers __read_mostly; // !0 = provide stall notifiers
(rarely useful)
EXPORT_SYMBOL_GPL(rcu_cpu_stall_notifiers);
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL-PREEMPT
b/tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL-PREEMPT
new file mode 100644
index 0000000000000..8230b14bfe680
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL-PREEMPT
@@ -0,0 +1,12 @@
+CONFIG_SMP=y
+CONFIG_NR_CPUS=8
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=y
+CONFIG_HZ_PERIODIC=n
+CONFIG_NO_HZ_IDLE=y
+CONFIG_NO_HZ_FULL=n
+CONFIG_DEBUG_LOCK_ALLOC=n
+CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
+CONFIG_RCU_EXPERT=y
+CONFIG_TRIVIAL_PREEMPT_RCU=y
diff --git
a/tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL-PREEMPT.boot
b/tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL-PREEMPT.boot
new file mode 100644
index 0000000000000..299cd3a12df6c
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL-PREEMPT.boot
@@ -0,0 +1,3 @@
+rcutorture.torture_type=trivial-preempt
+rcutorture.onoff_interval=0
+rcutorture.shuffle_interval=0
--
2.40.1
